1. Field of the Invention
The present invention relates to an ink ejection amount measurement method and an ink ejection amount measurement system, and more particularly, to an ink ejection amount measurement method and ink ejection amount measurement system whereby the ink ejection amount can be measured accurately even using an image reading device of low resolution in an inexpensive system.
2. Description of the Related Art
In inkjet recording apparatuses, it is important from the viewpoint of stabilizing print quality that the ink ejection amount should be uniform from each of a plurality of nozzles formed in a recording head. Therefore, it is sought to achieve accurate measurement of the amount of ink ejected from each of the nozzles during maintenance, or the like.
Therefore, a conventional method for measuring very small droplet amounts, such as those of colored inks, uses either an ink droplet amount measurement method based on a weight measurement method, or a droplet amount measurement based on a light absorption method.
An ink droplet amount measurement method based on weight measurement involves first ejecting ink for a prescribed time period at prescribed time intervals, and then measuring the amount (weight) of ink used during that time period, by means of a chemical balance, or the like. Thereupon, the average liquid droplet amount (average ejection amount) per ejection is determined by dividing the amount of ink used by the number of ink ejections performed.
Furthermore, a droplet volume measurement method involves firstly sealing the ink inside a transparent container, and then radiating light of a certain intensity to one side and measuring the light passing via the opposite side (light absorption rate). Thereupon, since the light absorption rate is known to be directly proportional to the ink density (according to Lambert-Beer law), then the ink density is determined by means of this method. In order to measure the droplet volume, an observation amount graph which indicates the relationship between the ink density and the ink ejection amount is determined previously, the droplet volume is calculated from the ink density thus obtained, and the average ejection amount per ejection operation is determined by dividing the droplet volume by the number of ejection operations.
Japanese Patent Application Publication No. 9-48111 and Japanese Patent Application Publication No. 10-230593 disclose the technique in which, the correlation (calibration curve) between the density and droplet volume is previously determined according to a method based on light absorption, the apparatus is on line, a transmission light source and a CCD are used in such a manner that the (transmitted) luminance (the reciprocal of the density) is measured by the CCD, and the ejection amount per nozzle is measured instantly from the calibration curve.
Japanese Patent Application Publication No. 9-48111 and Japanese Patent Application Publication No. 10-230593 teach an embodiment using a CCD camera which outputs 256 tonal levels (8-bit) having pixel density from 0 to 255, but it makes no mention of the minimum pixel resolution of the CCD camera. Consequently, if the minimum pixel resolution of the CCD camera is a low resolution, then the pixel resolution also varies. Furthermore, if it is sought to measure the ink dot diameter with good accuracy by means of a CCD camera or scanner having low resolution, then it is necessary to prepare a separate test pattern.